In cavity wall construction, an inner wall portion or wythe is usually made of wood or steel framing sheathed with gypsum board or other sheet material, or concrete block. Insulation board is often applied to the outer side of the concrete block or sheathing and ordinary interior finish materials to the interior side of the inner wythe. A second wythe is constructed using the desired exterior finishing material (usually brick) which covers the insulation or sheathing. The facing sides of the two wythes are typically separated two to four inches to form a cavity; the cavity provides an air space and may include insulation.
Regardless of the material used in construction of the wythes, it is essential that an air space be maintained between them; it is also essential to provide a way to remove moisture from the cavity. Drainage holes called "weeps" are normally provided at the first course of brick above grade elevation, at lintels and at other flashings which direct water away from the interior of the building. Moisture can enter the cavity due to condensation, permeation, plumbing faults, roof faults, and cracks in the masonry which inevitably occur over time, among other ways. It is impossible to prevent small amounts of water from penetrating brick or other masonry walls because the materials are porous and prone to cracking. If water accumulates in the cavity between the inner and outer masonry portions of a wall, problems with degradation of the brick, efflorescence, interior damage, and damage to foundations can develop.
A common problem in cavity wall erection is that excess mortar and other construction debris may fall into the cavity and create places where moisture can accumulate. If mortar or other construction debris obstructs the weeps or provides a place where water can pond, the build-up of moisture can damage insulation, carpets, interior wall finishes and furnishings. Efflorescence is another problem resulting from accumulation of water in the wall. In addition, the freezing of accumulated moisture can cause spalling and other damage. A variety of techniques have been attempted to prevent air spaces, vents and weeps from becoming blocked, but none has proven adequate.
One technique to keep the cavity wall air space open is to increase its size. However, that necessarily results in increased foundation size, thicker walls, more expensive window and door installation, and greater labor costs. Other common techniques also have serious drawbacks.
For instance, the cavity is sometimes filled with pea gravel to prevent dropped mortar from filling the weeps. Pea gravel itself will sometimes block the weeps or else simply raise the elevation at which mortar accumulates to the height of the pea gravel. The installation of pea gravel is laborious, especially as the wall increases in height.
Another technique requires construction workers to lift a board through the cavity to dislodge and remove dropped mortar. In the course of lifting a board through the cavity, the board may catch on bricks which have partially set and compromise the integrity of the bond of the mortar to the brick. The technique is also disruptive of the normal work of the mason and is difficult to accomplish when horizontal joint reinforcement materials are incorporated into the wall design.
Another technique is described by Ballantyne in U.S. Pat. No. 4,852,320 and requires the mason to install inclined shapes of sheet or extruded metal within the air space of the cavity wall. In U.S. Pat. No. 5,230,189, Sourlis describes shapes made of polymer mesh for catching mortar debris as it drops into the wall cavity. Although such techniques may represent an improvement over traditional methods, they do not overcome all of the traditional drawbacks. First, the on-site installation is difficult to properly supervise because the components are hidden from view almost immediately after installation. In the event that problems with the installation are discovered, correction is likely to be expensive, perhaps prohibitively so. Second, the techniques and equipment are designed to trap and collect debris. Once collected, that debris could, in some instances, provide locations water may accumulate with the potential for damage to the structure. Another shortcoming of previous attempts to solve the problem is the expense of implementing them. Most are relatively unproven and represent a substantial initial expense to obtain an uncertain benefit.
What is needed, then, is a way to keep excess mortar and other construction debris out of the air space from the very beginning. The present invention meets that need by preventing, from the outset, creation of excess mortar debris which could block the weeps and allow moisture to accumulate, and excluding other debris from the cavity by preventing it from entering in the first place. Not only does the present invention prevent blockage of weeps, it also prevents bridging of masonry ties with mortar. It is expected to reduce construction costs by allowing smaller cavity dimensions which can reduce the cost of foundations and window and door openings. It is especially significant that the present invention is expected to reduce the cost for mortar by reducing waste while increasing productivity. The present invention also allows the specification of smaller air spaces thereby providing space for additional wall insulation and/or smaller foundation sizes.
The present invention is comprised of a continuous fluid conducting medium to assure both that air can circulate in the air space and that water can be safely and reliably removed; the fluid conducting medium believed preferable is a coarse polymer mesh or non-woven fabric. Such a mesh would be analogous to the non-woven materials sometimes used for filtration of air in forced-air furnaces. The fluid conducting medium is not to be water absorbent and must have sufficient rigidity and strength to hold mortar which comes into contact with it until the mortar is set. By holding the mortar in the interstices of the mesh, the fluid conducting medium thereby prevents the mortar from accumulating at the bottom of the cavity wall airspace and causing blockage of weeps. Additionally, mortar and construction debris are precluded from entering the cavity airspace to any potentially troublesome extent by the mesh which extends largely continuously throughout the air space. The fluid conducting medium is preferably attached to extruded polystyrene foam insulation board or equivalent and together with the insulation, substantially fills the air space of the cavity wall.
With or without insulation, the fluid conducting medium is attached to the first wythe (the inner wythe) and disposed within the air space at a distance of approximately 1/8" from the inner surface of the second wythe (the exterior wythe). The mortar expressed from the inner side of the bricks as they are laid will be prevented from falling because it would become entangled in the mesh fibers. The expressed mortar would not extend across all of the distance from between the second wythe and the first wythe whether it is fitted with insulation board or other sheathing material. Thus, an uninterrupted channel will be maintained from the top to the bottom of the wall cavity and throughout the entire length of the wall to assure proper moisture drainage and air circulation. Some design professionals specify installation of vents both at the brick ledge (weeps) and at the top of the wall or below relief angles.
The fluid conducting medium must allow circulation of air and the free drainage of moisture. Although it is preferably fabricated of a polymer mesh, other materials and configurations could be used effectively to achieve an equivalent result. Other configurations which may prove equivalent could include fluid conducting medium made by forming grooves or protrusions on sheets of insulation or other construction materials such as gypsum board. It is possible that the fluid conducting medium may be made of recycled or mixed recycled plastic. Although other techniques may be used to form the fluid conducting medium, it is believed preferable to form a non-woven polymer mesh having a thickness twice that desired. The mesh could then be split to half thickness using a hot-wire cutting device or the like. The resultant comparatively sharp ends may hold expressed mortar more securely than the other side of the mesh.
It is to be understood that, although the fluid conducting medium is preferably bonded to insulation sheet material in the facility where the product is manufactured, it may also be pressed into place at the construction site or affixed using any suitable adhesive. It is anticipated that sheets of fibrous mesh fluid conducting medium could be installed by placing them between the masonry ties. It is further to be understood that the preferred resilience and strength of the material will be sufficient to allow it to hold mortar but also soft enough to permit workers to readily install masonry ties and to otherwise work with it easily.
A further advantage of the invention disclosed herein is that it provides a method for equalizing air pressure throughout the cavity wall. When wind is blowing, the pressure on the down-wind side of the building is less than the pressure on the up-wind side. If the outside of the building is wet, for example due to rain, the existence of any significant pressure differential will cause water to be drawn from the outside of the building through even very small cracks, defects, and other openings in the masonry. The present invention, by preventing any obstruction of the cavity air space vents or the weeps, allows air pressure to equalize at all points on both sides of the outer wythe. The presence of obstructions in the air space or weeps can result in wet spots during rains which can be very difficult to correct.
The invention is expected to improve the overall quality of the constructed building. The expected improvements include reduced re-work, fewer complaints by owners, and longer building life. The cost of the materials used in the invention are offset by savings resulting from reduced mortar waste, reduced foundation size, lower costs to construct window and door openings, reduced costs for steel members such as lintels, and improved productivity. Unlike those approaches intended to collect construction debris which enters the cavity air space, the present invention may lower overall construction costs; that benefit is complemented by easier installation and improved quality of the final product.
The drawing shows a typical installation with brick exterior finish, a clearance space of 1/8", a mesh thickness of 3/8", an insulation layer of 11/2", and an interior structural masonry wall of concrete block. In this way, a 2" cavity can provide all benefits of cavity walls having a 4" cavity at a much lower cost. It is believed that the mesh thicknesses most commonly used will be in the range of 3/8" to 1" although other thicknesses could be used in certain applications.